Pedestrian Bridge, Japan. †

1.Field of application

A pedestrian bridge across a prefectual road, Japan(Fig.1).

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Fig.1 Pedestrian bridge

2.Circumstances of Repair

A Serious fracture that extended halfway through the circumference of a steel pipe column was discovered in a pedestrian bridge.

3.Types of structure

The center span of its superstructure is 10.5m and it is supported by two steel pipe columns. The diameter of steel pipes is 609.6mm, its plate thickness is 9.5mm and its height is 4.7m(Fig.2).

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Fig.2 Elevaion of pedestrian bridge

4.Details of loading

Traffic of vehicles passing under the pedestrian bridges and pedestrians on the pedestrian, wind and so on.

5.Description of damage

The fracture was observed in a steel column ‘P1’ in Fig.2. Fig.3 shows a photograph of the fracture in the steel pipe column. It was found that the fracture extended halfway through the circumference of a steel pipe column. Fig.4 indicates the condition of boxing welds around the rib plates on the steel pipe column and results of magnetic particle tests at the boxing weld. In Fig.4, ‘E-rib’ was defined as a rib plate located in the fractured area. As shown in Fig.4, the quality of welds at both rib plates was very poor and traces like Luder’s bands were observed around ends of both rib plates. Fig.5 shows an example of the damage found in the superstructure. The damage shown in Fig. 5 was similar to the damage caused by car crash.

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Fig.3 Fracture in the steel pipe column


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Fig.4 Condition of boxing welds around ribs


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Fig.5 Damage found in the superstructure


6.Repair method applied

Fig.6 shows the repair method. Stop holes were bored for removing the tips of the fracture and preventing the crack propagation. Pieces around the boxing welds of E-rib and W-rib in the cracked area were removed because cracks were found and they were used as test specimens or samples for the investigation of crack surfaces and material properties.Fractured pipe column was retrofitted with bolted splice rings and plates as shown in Fig.19.The thickness of splice rings is 12mm. In respect of connecting splice rings and plates with bolts, high strength blind bolts were used because the diameter of steel pipe column was too small for workers to fasten bolts in it as shown in Fig.7 .

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Fig.6 Retrofit work


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Fig.7 Steel pipe column after retrofitting
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